SCC-I hidden potential unlocked?

Prophet (3849)

01-11-2020, 05:40

Yeah I read about those techniques in another thread. Cool stuff Given there is enough memory could vgmplay do the compression in memory and then play the compressed/optimized code? Could that improve playback accuracy or have any other benefits?

Van Grauw

Ascended (10707)

01-11-2020, 12:36

Since the compression algorithm is “off-line” (although on-line variants exist, e.g. LZ78), the entire track needs to be loaded into memory before it can be compressed. Furthermore the structures for performing the compression use a lot of memory (think 10x-30x). The compression itself, although linear in time to the size of the input, will be slow on a Z80.

So I don’t think it’s useful to perform this compression on MSX. In my opinion the best pipeline for a replayer is - record VGM output from anything - convert the VGM to a compressed custom format on PC - play back with simple and fast MSX player.

And to respond briefly to SCC playback in VGMPlay (off-topic), to improve playback accuracy the key is not the compression but to combine consecutive SCC waveform writes into a single command. I.o.w. to rewrite the command stream into something more efficient to process. See here.

Van niek

Expert (112)

09-11-2020, 23:10

vgm_rec had a bug I now learned, the SCC+ part of the MegaFlashROM_SCC+ was detected as a normal SCC, so no audio recording. Fixed that; so now I have a VGM file from the corridor of time. At least part of it; it becomes a MB pretty soon, it sure does some funky stuff

But even with a 130 kB VGM file I get out of memory when using msxdos2 to start vgmplay on a Boosted MSX2 (512kB). It's probably because I'm doing something wrong @Grauw?

I know, I know, it probably won't work but I'm just curious.

BTW the Corridor drums are not on the normal PSG, so must be on the extra PSG of MegaFlashROM_SCC+, no recording for that... yet...

Van Grauw

Ascended (10707)

09-11-2020, 22:54

Hmm no I don’t know what that could be. Is the VGM file 130 kB uncompressed? Because that should just fit on an MSX with 512k RAM. You can check how much memory DOS2 has available using the tools MEM.COM, MAPMAP.COM or MAPINFO.COM.

By the way, I’m considering turning my gngplay project into a more generic replayer framework which also supports PSG + MSX-MUSIC and PSG + SCC. It would have fast portable replayer code for each of those chip combinations, with support for ROM banking and compression. It would work regardless of what the music is composed with as long as you record a VGM of it.

p.s. Can you mail me the VGM of Corridor of Time for me to test with?